Final answer:
Cdc6's role during S phase is to d. bind to ORC and recruit DNA helicase, aiding the initiation of the DNA replication by unwinding the DNA double helix.
Step-by-step explanation:
The function of Cdc6 during S phase is to d. bind to the Origin Recognition Complex (ORC) and recruit DNA helicase, which is vital for the initiation of DNA replication.
Cdc6 is a regulatory protein that works alongside other proteins to ensure proper DNA replication.
Specifically, Cdc6 attaches to the pre-replicative complex (pre-RC) at origins of replication and helps load the helicase onto the DNA strand, which then unwinds the DNA double helix, allowing replication to begin.
This process is critical to ensure that the DNA is replicated once and only once within the S phase of the cell cycle.